Electron discharge device



Oct. 27, 1936;

T. M. SCHRADER ELECTRON DISCHARGE DEVICE Filed July 12, 1932 2 Sheets-Sheet 1 iNVENTOR TERRY M SHRADER ATTORNEY @117, 1936. M SCHRADER. 2,058334 ELECTRON DISCHARGE DEV-ICE Filed July 12, 1932 2 Sheets-Sheet 2 TERRY M SHRADER BY ATTORNEY Patented Oct. 27, 1936 2,058,834 ELECTRON DISCHARGE DEVICE i v I Terry M. Shraden West Summit, N. 3., assignmto Radio Corporation of America, a corporation of Delaware Application July 12, 1932, Serial No. 622,140 8 Claims. (or. 250- 275) My invention relates to devices for the reception of modulated high frequency oscillations, such as radio signals, and more particularly to an electron-discharge tube and associated cir- 5 cults for obtaining improved reception, detection, amplification and control of modulated high frequency oscillations with less apparatus than has heretofore beenused. v

A diode, or two electrode tube having a ther- 0 mionic cathode and a plate, and connected to act as a rectifier which permits high frequency oscillations to flow in one direction but not in the other, is the simplest form of detector for radio signals and similar high frequency oscillations, and also has many other useful applications in radio reception. The plate load can conveniently be made of such impedance that the current flowing between the cathode and the plate is almost directly proportional to the applied voltage, hence there can be derived from the plate circuit a rectified voltage which varies directly with variations of the applied voltage, and detection with practically no distortion can be obtained. I

reception, but since it is a simple rectifier, its output voltage is no'higher than the input or signal voltage. For use. with a loud speaker the diode detector is associated with an amplifier to increase the output voltage. Both radio and audio frequencies appear in the output circuit of the diode, and a filter circuit must be used to remove the radio frequencies, unless two diodes, connected 'in push pull circuit, are used as a detectors A diode' may also be used for volume control by connecting it to vary the sensitivity of a re-- ceiving set so as to keep the volume'fairly con stant for signals which diifer greatly in strength. This volume control may be secured by applying to the grids of one or more of "the amplifying tubes of the set a unidirectional voltage which decreases the sensitivity of the tubes to an extent dependent on the increase in the strength of the signal. The uindire'ctional voltage for volume control may be obtained by rectifying the high frequency carrier wave by a diode to obtain a unidirectional voltage which varies with the strength of the carrier wave, and applying this voltage to the amplifier grids to make them more negative as the carrier wave becomes stronger, thus changing their bias enough to make the amplifier correspondingly less sensitive. 7

tube.

The diode used as a detector gives high quality Since a detector comprising an amplifier and one or two separate diodes with the associated apparatus is rather complicated and expensive, it has been customary to use for detection a triode with the circuits such that the triode 6 rectifies and also amplifies the signals. A triode detector with combined detection and amplification is sensitive, but causes some distortion even at low signal strength. This distortion becomes 'worse as the signals increase in strength and lb the plate detection tends to counteract the grid detection. In spite of this distortion the simplicity and sensitiveness of the triode detector are of enough advantage to warrant its use for many purposes. 16,

One object of my invention is toprovide an electron discharge tube which is a combined detector, amplifier, and automatic volume control tube, and is capable of use in many ways and in namy combinations to give results that no heretofore could not be obtained with a single Another object is to provide such an electron discharge tube which is an amplifier no larger than the usualamplifying tube of the same amplifying capacity, yet has in addition the 25 capabilities and usefulness of two independent diodes. A further object is to provide circuits in which tubes constructed in accordance with my invention may be utilized to advantage.

In accordance-with my invention I provide e single electron discharge device which isme- 'chanically a unitary device, but functionally is an amplifying triode associated with, and 8. rectifier having two anodes which are electrically independent of each other and of the amplifier. 35 Such a device has many applications and a very great flexibility for use with many d-iiferent kinds of circuits because of the electrical independence of the" diodesand the amplifier. The rectifier may be operated as a full wave rectifier, or as two independent half wave rectiiiers'used for dif ferent purposes; "for example, one may be used as a detector and the other for automatic voluine control. The elements of the device are enclosed in a single bulb and are combined in; single mount having a common cathode, withthe I grid and plate of the amplifier surrounding the cathode near one end, and the rectifier anodes mounted near the other end on independent leads. 50 I may insure the complete electrical independence of the rectifier and the amplifier by means of a partition, preferably an electro-static shield, interposedbetween the rectifier assembly and the triode assembly, and preferably connected to the u cathode. This shield may to advantage be made in the form of a metal hood covering and surrounding the rectifier.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however both as to its organization and method of operation will best be understood by reference to the following description taken in connection with the accompanying drawings in which Figure 1 is a longitudinal section of one form of a tube constructed in accordance with my invention; Figure 2 is a cross section along the line 2-2 of Figure 1, showing a plan view of the upper end of the triode assembly; Figure 3 is a cross section along the line 3-3 of Figure 1,

showing the rectifier and the electro-staticshield around it; Figure 4 is a cross section along the line 4-4 of Figure 1; Figures 5 and 6 are schematic diagrams of circuits in which the tube may be used as a full wave detector, with the amplifier in Figure 5 biased by the rectifier, and in Figure 6 biased by a battery; and, Figure 7 is a schematic diagram of a circuit in which the amplifier has a fixed bias, one diode is used for detection and the other for automatic volume con trol.

The tube illustrated in the drawings as one embodiment of my invention comprises a sealed highly evacuated vessel, preferably a glass bulb in having at the top a cylindrical dome II and with the usual base l2 at the bottom. The bulb has a reentrant stem II with a fiat press Il on which the electrodes are mounted to form one assembly constituting an amplifier, such as a triode, and also another assembly constituting a rectifier with two anodes, or two diodes. The two assemblies, although a structural unit, are electrically separate and distinct, with each rectlfier anode having its own individual connection and comprises a sheet metal amplifier anode or plate electrode I! in the shape of a tubular cylinder with two diametrically opposite longitudinal wings, a tubular cylindricalgrid electrode i6, and an electron emitting electrode such as an indirectly heated unipotential cathode coaxial with and surrounded by the grid and plate electrodes. The cathode preferably comprises a metal cathode sleeve ll extending lengthwise of the bulb and containing a heater, such as a reverse coiled helix of tungsten wire with its two ends projecting from the lower end of the sleeve I1 and connected to a pair of heater leads in the press. The electrodes of the triode assembly are carried on the stem by two support rods II which extend from thepress and engage the anode wings, and also carry the grid and cathode on two insulating bridges or spacers l9 and 20 extending between the rods ll near the ends of the plate electrode It. The top spacer l9, preferably a cruciform sheet of mica, fits into the dome ll well enough to prevent lateral movement of the mount. The lower spacer is preferably an oblong sheet of mica. The two spacers are held in place at the ends of the plate by metal bands 2! which clasp the spacers and are secured to the wings of the plate. The cathode sleeve and the side rods of the grid fit into holes in the mica spacers and are held in place by the spacers. The cathode sleeve is considerably longer than the triode assembly and projects through the lower spacer 20 to a point considerably nearer the stem. This projecting,

portion or lower end of the cathode sleeve is the of a strip of sheet metal extending either part way around the cathode sleeve, or preferably, as shown in the drawings, completely around it to form a ring anode. These two ring anodes are spaced along the projecting portion of the cathode sleeve, andare electrically independent of each other and of the triode. A cathode lead 24 extends through the press near the rectifier anode leads", and is electrically connected to the lower end of the cathode sleeve, preferably by a connector 25. The rectifier anodes 22 may be very much smaller than those of the rectifying tubes generally used in receiving sets since very small currents of sufiicient rectified voltage will give the desired results.

The cathode sleeve is coated with some material, such as barium and strontium oxides, of high thermionic emissivity, on those portions in registry with the plate It and with the rectifier anodes 22, the intermediate portion near the lower spacer 20 preferably being left uncoated to avoid the effects of stray emission from this portion.

In some cases it may be desirable to shield the rectifier and the triode from each other, and this may be done by interposing a partition of some kind between the two assemblies. Mechanical shielding by a disc or sheet may be employed, but I prefer to also shield electrically by using a metal partition, preferably grounded. I have found that good shielding can be obtained by meansof a metal cylinder around the diode, particularly if made in the form of a metal hood II which covers the rectifier assembly. This hood is conveniently mounted on the press, preferably by a support 21 and may be steadied by the cathode lead- 24.

A tube constructed in accordance with my invention has the capabilities and usefulness of an amplifier and two separate diodes, and permits the commercial use of many desirable circuits, combinations and hookups. As examples of some of the many such circuits which may be used, I have shown some typical circuits. In the circuits shown in Figures 5 and 6, the tube operates as a full wave detector, and also, in Figure 5, as a diode biased amplifier, and in Figure 6 as a fixed bias amplifier. As shown in Figure 7, each diode may also be used as a half wave rectifier, one diode being used for detection and the other for automatic volume control.

In Figure 5 the tube is shown with the cathode heated by current from a transformer It. The plate circuit from the plate I! to the cathode includes a source of energy, such as a battery 20 and an impedance, such as a load resistance II. The rectifier anodes 22 are connected with the terminals of an oscillatory circuit 3| comprising suitable tuning means, such as a variable capacitor 32, and a coil or fixed inductance 38. Signals to be received are impressed on the circuit by any suitable means, such as a coupling coil 34 connected with a collector of radio fre quency energy.

The oscillatory circuit II has a midtap or center tap 35 connected by a grid lead or gridconnection 36 to the control grid of the amplifier,

and also by a cathode lead"or connectioni'l'l' to the cathode sleeve i'l through, a resistor. 38,

shunted by a radio frequency by-passcondense r 39. Both half waves of the modulated signal impressed on the circuit 3| are .rectifled, produc ing atthe center tap 35a full wave rectifiedvoltage which is a resultant of the'radio frevoltage appear across the resistor 3.8 V For auto matic volume control an automaticvolumecontrol lead 40 is connected to the center tap, and by means of a resistor 4|, and condenser 42 the audio frequency component is, filteredout so that only unidirectional voltage is delivered by the, lead 40 to the automatic volume control. The audio frequency component of the voltage on the center tap 35 is applied to 'the grid of the triode through the grid connection 36, and is amplified in the usual manner. I

Figure 6 shows a circuit in which the amplifier has a fixed bias, obtained by a biasing battery or from a fixed voltage tap on the direct current supply, as is customary. The connections are as in Figure 5, except that the grid circuit, which includes a biasing battery 43, a resistor 44, and a grid connection 45 to the control grid I6, is coupled to the center tap 35 through a coupling condenser 46 which carries audio frequency from the oscillatory circuit to the grid circuit. The plate circuit may include a coupling transformer 41 instead of the resistance 30.

Figure '7 shows a circuit for using one diode for detection and the other for automatic volume control. In this circuit the coil 33 is split into halves, the outer ends of the halves being connected to the anodes 22 and the inner end of each half being provided with a separate return to the cathode through a resistor 38 and a bypass condenser 39, thus providing a circuit 48 from one anode to 22 to the cathode, and a circuit 49 from the other anode 22 to thecathode. In the circuit 48 the by-pass condenser 39 passes radio frequency only, and the audio component of the signal voltage in the circuit is passed to the fixed bias grid circuit by the coupling condenser 46. In the circuit 49 the by-pass condenser passes both audio and radio frequencies, and the unidirectional voltage appearing in this circuit is applied to the automatic volume control lead 40. The circuits 48 and 49 may be provided with a condenser 50 between the halves of the coil 33 and a variable condenser 5| for tuning the two circuits to the desired frequency.

While I have shown and described the preferred embodiment of my invention, it will be apparent that many modifications may be made in the structural details employed for carrying my invention into effect without departing from the scope thereof, as set forth in the appended claims.

Having thus described my invention, what I claim is: 4

1. An electron discharge device comprising a sealed vessel enclosing a triode assembly comprising a plattfia grid, and an elongated unipotential cathode coaxial with said plate and projecting from one end of said triode assembly, a diode comprising an anode adjacent the projecting end of said cathode, a conducting lead constituting the sole support for said anode, and a metal hood over the projecting end of said cathode and covering and surrounding said anode.

2. An electron discharge device comprising a sealed vessel enclosing a triode assembly compris ing an elongatedlunipotential cathode, agrld and, a plate coaxial with and surrounding said Cathode for a'portion of its length to leave the end of said cathode projecting from saidtriode assembly, a

diode comprising an anode adjacent the project ing end of said cathode, a metal hood over the projecting end of saidcathode andcovering said anode, and'a conducting lead extending inside said hood and oonstituting the sole, support for 1 said anode. i i i 3. An, electron discharge device comprising a stem, two parallel support rods projecting irom said stem, a tubular plate secured to, and carried by at least one of said rodstcp and bottom in sulatiug spacers extending between said rodsadjaceut the top and bottom ofasaid anode, a

. grid inside and coaxial with said anode antic mprising two parallel side rods supported by said spacers, a uni-P tential cath de comprising 'a heater on said stem and an oxide coated metal sleeve surrounding said heater and mounted on said spacers with one end projecting through said bottom spacer, a plurality of anodes mounted on said stem adjacent the, projectingend of said cathode and below said bottom spacer, and'a conducting lead in said stem for each anode constituting the sole support of said'an'ode.

4. An electron discharge device comprising a sealed bulb having a reentrant stem and enclosing amplifier electrodes comprising a tubular amplifier anode and a coaxial tubular control grid mounted on saidstem with their longitudinal axes in alignment withsaid stem, a rectifier anode mounted on said stem and electrically independent of said amplifier electrodes, said rectifier anode being spaced far enough along the longitudlnal axis of said amplifier electrodes to be be! yond their end, leads extending through said stem to form an independent electrical connection for each of said amplifier electrodes and for said rectifier anode, and a single straight elongated cathode common to said amplifier electrodes and to said rectifier anode and mounted on and in alignment with said stem and having a portion near one end surrounded by and coaxial with said amplifier electrodes nda different and dis, tinct portion near the 0 her end adjacent said rectifier anode.

5. An electrone discharge device comprising a sealed vessel having a reentrant stem and enclosing a cathode comprising a straight equipotential electron emitting sleeve mounted on and in alignment with said stem, a set of amplifier electrodes comprising a control grid and a plate both shorter than said cathode sleeve andunconnected within said vessel to aid cathodeand mounted coaxially of said cat ode to completely surround said cathode sleeve for only a portion of its length near the end remote from said stem, a rectifier anode mounted on and adjacent said stem to co-. operate with a different and distinct portion of said cathode slee've near the other end thereof and spaced lengthwise of said cathode to be electrically independent of and separated from said amplifier electrodes, and a metal shield connected inside said vessel to said cathode sleeve and mounted on said stem adjacent said rectifier anode to form an electrostatic shield between said rectifier anode and said amplifier electrodes.

6. An electron discharge device comprising a sealed vessel enclosing a straight equipotential cathode which is common to both said assemblies,

said amplifier assembly comprising a grid elec- 1 trode and a plate electrode unconnected within said vessel to said cathode and mounted coaxial with and surrounding said cathode for only a part of its length near one'end to leave a different and distinct part of said straight cathode projectingilongitudinally from said amplifier assembly, lead wires constituting the sole electrical connections for said grid electrode and for said plate electrode, said rectifier assembly comprising two annular rectifier anodes mounted side by side and coaxial with said different and distinct projecting portion of said cathode and electrically independent of said amplifier assembly, two separate anode leads constituting the sole electrical connections for said rectifier anodes, and a metal shield surrounding said rectifier anodes and connected within said vessel to said cathode.

7. An electron discharge device comprising an evacuated envelope containing an indirectly heated cathode, a tubular anode surrounding one end of said cathode, another tubular anode surrounding another portion 012 said cathode, said other portion of said cathode being coated with an electron emlsslve coating, and a sheet of mica strapped to said first mentioned anode to extend transversely of said envelope with its. ends engaging the inner wall of said envelope i'or spacing said first mentioned anode from the inner wall of said envelope.

8. An electron discharge device comprising an evacuated envelope, an electrode assembly within the envelope including an upper cathode, a lower cathode, and a common heater for rendering both said cathodes emissive, a plurality of electrodes surrounding the upper cathode, a plurality of electrodes surrounding the lower cathode, and a sheet of mica carried by said assembly and extending transversely of said envelope with its ends engaging the innerwall of said envelope.

- TERRY M. SHRADER. 

